Studies of the immunological processes, especially autoimmunity, underlying intraocular inflammatory diseases suggest the presence of several immunopathogenic antigens in the retina, retinal pigment epithelium, choroid and optic nerve. Thus far, only one of these antigens has been sufficiently purified and conclusively demonstrated to be uveitogenic; retinal S-antigen. Little quantitative work on the structure of S-antigens has been reported and its putative identification as rhodopsin kinase is uncertain. We propose to continue characterization of S-antigen immunochemically and to determine its primary structure. Knowledge of its sequence and antigenic determinants could lead to the development and use of haptenic peptides or analogues therapeutically. Because S-antigen is so potent in its effect, other candidates for immunopathogenic ocular antigens are properly suspect and exceptional measures to ensure that their activity is not due to contamination with S-antigen are required. A consequence of the ease of isolation and solubility of S-antigen is that investigation of other potential antigens is not being vigorously pursued despite abundant circumstantial evidence. This is especially true of membrane bound proteins which are much more difficult to study. Recent evidence from our lab suggests that examination of the membrane bound fraction of proteins from the rod outer segments is long overdue since it appears to be an unusually rich source of antigenic proteins other than S-antigen and rhodopsin, another putative uveitogenic antigen. We propose to isolate rod outer segments and purify two additional proteins from them, p35 and p27. Since we have evidence that p35 is also recognized by serum antibodies from some uveitis patients, it would be most interesting to isolate these proteins in sufficient quantity to test them for immunopathogenic activity in animal models. If S-antigen is demonstrated by vision researchers to be rhodopsin kinase, then the structural information to be gathered in this proposal will also contribute to the understanding of that enzyme and its function.